The invention relates to a method for coding of signal scanning values, making use of vector quantization and, more particularly, to a method of coding speech signals by vector quantization.
A CELP speech coding method is known from "Speech Communication" 8 (1989), pp. 363 to 369, wherein the coder parameters are optimized together. In comparison with sequential optimization, it is possible to considerably reduce the length of the excitation codebook.
A digital speech coder is known from WO 91/01545, wherein excitation vectors entered in a codebook are accessed for selecting an excitation vector which best represents the original speech scanning value. Two excitation vectors from two respective codebooks are employed for describing a scanned speech value in the speech coder in accordance with WO 91/01545. First, a first excitation vector is selected there independently of pitch information. The second excitation vector is selected in a corresponding manner. During orthogonalization of the second excitation vector from the second codebook, the resulting vector as well as the first selected excitation vector from the first codebook are taken into consideration. This selection process is then repeated with an orthogonalized excitation signal from the second codebook in order to finally identify those excitation vectors which best match the original speech scanning value.